The present invention relates to an image forming apparatus which automatically feeds a plurality of simplex documents one by one and transfers images of the fed documents successively onto both surfaces of copy paper sheets.
Japanese Unexamined Patent Publication No. 57-212460 discloses an image forming apparatus capable of making duplex copies from simplex documents. In the apparatus, the simplex documents set in an automatic document feeder (hereinafter referred to as an ADF) are automatically fed to be exposed, so that an image of one document is transferred onto a front surface of a copy paper sheet and an image of the next document is transferred onto a rear surface of the same copy paper sheet. Here, the front surface and the rear surface of the copy paper sheet mean respectively a first surface and a second surface of the copy paper sheet onto which document images are transferred successively.
In the above image forming apparatus, in the case where an image of a last document is transferred onto a front surface of a copy paper sheet, the copy paper sheet is retained in an intermediate tray provided in the image forming apparatus. Accordingly, there have been proposed the following two types of apparatus to handle the copy paper sheet retained in the intermediate tray with the front surface thereof copied with the last document image:
1) The copy paper sheet retained in the intermediate tray is forcibly discharged therefrom;
2) The copy paper sheet retained in the intermediate tray remains to be therein until a next document is to be fed in the ADF.
Incidentally, only a limited number of documents can be fed by the ADF. Accordingly, in the case where a great number of documents are to be copied, it is required that the documents are divided into a plurality of sets as to be fed by the ADF appropriately. However, in the image forming apparatus in which the copy paper sheet onto which the last document image is transferred is forcibly discharged from the intermediate tray irrespective of whether the last document image is transferred onto the front surface or the rear surface of the copy paper sheet, it is impossible to transfer an image of a first document of a next set fed in the ADF onto the rear surface of the last copy paper sheet of the preceding document set even if the last document image of the preceding set is transferred onto the front surface of the copy paper sheet. As a result, the copy paper sheet carrying the image of the last document of each set is destined to be wasted when the last document image is transferred onto the front surface of the copy paper.
On the other hand, in the image forming apparatus in which the copy paper sheet onto the front surface of which the last document image is transferred remains to be retained in the intermediate tray until the first document of the next document set is fed in the ADF, the following problem occurs. In the case where all the documents can be fed in one time, it is required that the copy paper sheet retained in the intermediate tray with the last document image transferred onto the front surface thereof be discharged therefrom with the use of a control key or the like, resulting in a cumbersome operation.